1. Field of the Invention
The present invention relates to surgical devices and methods for repairing tissue tears and, more particularly, to a device and method for repairing a soft-tissue tear in a knee.
2. Description of Related Art
The repair of soft tissue tears represents a persistent problem in orthopedic practice. It is known to apply sutures and various types of fixation devices to such tears.
Among the soft tissue sites that require fixation are the menisci of the knee. The material of the menisci is collagenous, and the fibers are oriented generally circumferentially. Posterior peripheral tears of the menisci may be treated by an open technique, wherein sutures are placed along the tear. An arthroscopic technique may also comprise placing sutures along the tear, but in this method through a cannula.
There are a number of fastener-type devices that are known in the art: Screiber (U.S. Pat. No. 4,873,976); Bays et al. (U.S. Pat. Nos. 4,884,572 and 4,895,148); Winters (U.S. Pat. No. 5,059,206); and Justin and Winters (U.S. Pat. Nos. 5,503,634 and 5,730,744). Bone screws are disclosed by Huebner et al. (U.S. Pat. Nos. 5,562,672 and 5,871,486).
It is an object of the present invention to provide a fastener, delivery device, and method for repairing a tear in soft tissue.
It is a further object to provide such a fastener that is made from a nontoxic, biocompatible, bioabsorbable plastic specially designed to maintain its structural integrity during the healing of the tear and to prevent tissue abrasion.
It is an additional object to provide such a fastener having a shape designed to compress the tear.
It is another object to provide such a fastener shaped to resist forces tending to pull apart the meniscal tear during healing.
It is also an object to provide such a fastener that resists stripping and has superior tissue retention characteristics.
These and other objects are attained with the fastener and delivery device system and method of the present invention, a fastener designed for repairing a tear in soft tissue of a patient, a particular exemplary embodiment comprising a meniscal tear in a knee, although this is not intended as a limitation. The fastener has a proximal end, a distal end, and a distal section having a narrowing cross section toward the distal end. In use an insertion of the fastener into soft tissue is facilitated by this narrowed distal end, which takes the form in a preferred embodiment of a generally conical-shaped distal tip.
The fastener further has a helical protrusion along a central section between the proximal end and the distal end. Along a distal section extending from the distal end, the helical pitch is substantially constant; along a central section between the distal section and the proximal end, the helical pitch decreases from the distal end to the proximal end. In use the decrease in the helical pitch along the central section can serve to bring two sides of the tear into apposition as the fastener is advanced across the two sides of the tear in a screwing motion. The substantially constant pitch along the distal section assists in preventing a stripping of the helical section.
At the proximal end is a head having a diameter greater than a major root diameter of the central section. The head is for improving the tissue retention characteristics of the fastener.
In an alternate embodiment of the fastener, the variable-pitch helical protrusion has means for resisting an axial force from pulling the fastener out of the tear and from pulling the two sides of the tear apart. Specifically, the resisting means comprises the helical protrusion having a buttress form.
In a preferred embodiment, the fastener material comprises a biodegradable plastic biocompatible with the soft tissue of the patient. The material is specifically designed to be biodegradable within a first time span greater than or equal to a second time span over which the sides of the tear can knit together. This feature permits the fastener to remain in place for as long as required for the tear to heal, but ultimately to biodegrade and be dissipated harmlessly into the patient""s system.
The material is further designed to have elastomeric properties compliant with those of the meniscus in order to confer biofunctionality.
A further feature of the present invention comprises a delivery device for introducing the above-described fastener into the area of the patient""s soft tissue to be repaired. A feature of the fastener permitting a mating with a delivery device comprises the fastener""s having an axial bore extending along the helical axis proceeding from the proximal end. The bore preferably has a noncircular cross-sectional shape so that an elongated driving device having a noncircular cross-sectional shape and dimensioned to pass into the bore can enter the bore and turn the screw. The fastener can then be advanced into the soft tissue by being rotated by the driving device in a direction having a handedness commensurate with the helically shaped protrusion. Simply put, the fastener appears as a variable-pitch screw that is internally drivable by rotation of an elongated member inserted into its bore.
The elongated driving device of the present invention for driving the fastener as described above has a distal end having means for mating with the fastener proximal end, and a proximal end having means for being rotationally driven. In use the fastener is mated with the driving device distal end, the fastener and distal end of the driving device are positioned adjacent the tear, and the means for being driven is rotated in a direction having a handedness commensurate with the helically shaped protrusion, thereby advancing the fastener across the tear.
In a specific embodiment of the system, the driving device further has a noncircular cross-sectional shape along a distal section adjacent the distal end. The fastener bore as described above has a noncircular cross-sectional shape dimensioned to permit the distal section of the driving device to pass into the bore and to permit relative axial sliding and rotational coupling movement therebetween. The axial slidability permits the driving device to be mated by sliding the driving device distal section into the fastener bore and to be removed once the tear has been breached by sliding the driving device out of the bore.
The method of the present invention is for repairing a tear in soft tissue of a patient. The method comprises the steps of providing a fastener having the features as described above. The fastener is then inserted into an area of soft tissue adjacent the tear. The distal end of the fastener is manipulated to a position generally normal to a long axis of the tear, and the fastener is driven across the tear in a screwing motion. The decrease in the helical pitch serves to bring two sides of the tear into apposition as the fastener is advanced.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.